depends if radiator is going to be replaced   if not gain access into cut back the pipes under floor level, cap off with either solder or compression blank end. this will probably neccesitate draining down the system or corking the system if open. or if you have quick fingers and a deft hand snatch the pipe by cutting with a wheely cutter and getting a push fit blank end over cut pipe QUICKLY however this method is not the best option  

regards

steve

Rads should be in parallel, not in series.   Otherwise turning one off turns all off.





~~~~I am not a plumber~~~~